Directional Airborne Networks
With the popularity of unmanned aerial vehicles (UAVs) and environment surveillance applications, airborne networks (ANs) have become important platforms for wireless transmissions in the sky.
Ku-Band Communications
The Ku-band of the electromagnetic spectrum (approximately 10-17 GHz) has been used, for example, for land-to-satellite communication applications. It can be useful for when satellites sends signals to a mobile object, such as train communications, aircraft Internet access, and the like. Ku-band satellites may require the relatively high gain of directional antenna in order to reach hundreds of miles away. The carrier-to-noise ratio (C/N) of Ku-band communication, even in rain (for example, 4 mm/h precipitation), can maintain a reliability of 90% and a bit error rate (BER) of 10−5, for a distance of approximately 200 km. Other methods have also been shown to achieve spectrum sharing in indoor applications, albeit in the 15.7-17.2 GHz band, in addition to showing that the impact of interference can be negligible in many spectrum sharing cases.
Overall, Ku-band communication has a path fading performance between the Wi-Fi case and milli-wave links. It has much better signal focusing capability than Wi-Fi, which means that a directional antenna can deliver the Ku-band signals for long distances without much diffusion. This can be called its “semi-wire” feature. By using multi-beam antennas, space reuse can be achieved, to make neighbors in different beams of a node communicate with a referred node simultaneously. The Ku-band's signal diffraction capability can be better than milli-wave due to its lower frequency, which means general small objects (such as a cat) cannot totally block its line-of-sight (LOS) communications. Ku-band signals can even get through the human body with certain path loss.
Multi-Beam Antennas
As per this disclosure, multi-beam antennas simply refer to an antenna that is able to separate the signals between different beams and can achieve concurrent sending or receiving in all beams. But, a multi-beam antenna may not allow some beams to send while some to receive in the same time. A multi-beam antenna may also not have the capability of using the feedback from a receiver to form an antenna array weight matrix. Thus, it might not be able to control the whole antenna to achieve a multiple-input and multiple-output (MIMO)-like smart communications.
Multi-Beam MAC Protocols
Many Media Access Control (MAC) protocols under directional antennas assume that the antenna has only one direction at each time, and few are geared towards multi-beam antennas.
Contention-based MAC in 802.11 networks have been studied. However, in this context, hybrid MAC (HMAC) have been proposed to achieve concurrent packet reception (CPR) as well as concurrent packet transmission (CPT). However, these studies only assume an 802.11 distributed coordination function (DCF) is used. This may not be suitable to some contemporary MAC implementations (such as 802.11e) that emphasize the use of point coordination function (PCF). PCF plays a critical role in quality of service (QoS)-oriented applications since it can use a point coordinator (PC) to poll each node in order to control their sending rates. Thus, PCF can support the QoS performance via the resource allocation and transmission scheduling among the nodes.
QoS-based MAC conducted in Wi-Fi has also been studied. In this context, a set of polling model control protocols have been used in order to schedule the transmissions of multiple nodes to a Wi-Fi access point (AP). Only PCF mode can be improved compared to standard 802.11 protocols. The DCF mode has not been explored in multi-beam antennas. Moreover, only the AP is assumed to make use of multi-beam smart antennas (MBSAs) while other nodes just simply use omni-directional antennas.
Distributed, receiver-oriented MAC with multi-beam antennas, have been designed previously as well. Unlike general Carrier Sense Multiple Access (CSMA)-based random access schemes, the use of on-demand handshakes and signal scanning has been avoided. Instead, node IDs are simply used to determine the transmission schedule. The studies however need 2-hop topology information, and many practical MAC issues are not considered, e.g. synchronization issues, QoS issues, and the like.
QoS in WMNs
QoS in wireless mesh networks (WMNs) is a well-studied topic considering so many works on the support of prioritized transmissions in ad hoc networks. However, most of existing WMN QoS works are conducted in higher layers. One reason for the lack of investigation on QoS support in lower layers may be due to the dearth of adjustable parameters in the MAC layer. The disclosed methods propose multiple enhancements to 802.11-like MAC in order to support QoS, such as Time Division Multiple Access (TDMA)-like collision domain separation, rate control in each beam, and the like.
Intelligent Beam Prediction
Intelligent node state prediction for improving MAC performance remains uninvestigated. Mission-oriented airborne networks may need careful communication planning, and mobility-adaptive data transmissions can be proactively scheduled based on the prediction of node behaviors.